1. Field of the Invention
The present invention relates to a data processor for generating character images, especially to an address transformation system in a character image generator of bit map type.
2. Description of the Prior Art
In a laser printer which provides a laser optical system and an electro-photographic system, there is usually used a so called bit map system as a character image generating system. In the bit map system, there is provided a bit map memory having a memory area for storing all image data contained in one page to be printed. Image data sent from an external data processor are stored as bit images temporarily in the bit map memory. If image data sent from the external data processor are character codes, individual character bit images are formed in the bit map memory by reading them from a font memory corresponding to character codes sent. This bit map system has advantages in that fine control with respect to a print format regarding print positions of images and an orientation of print is possible and images other than character images can be formed, although a bit map memory of a large volume and of a high cost is needed therefor.
Conventionally, a manner for accessing data by the bit map memory is determined according to a size of a print paper and a print resolution chosen.
For example, in a case wherein print is made on a print paper of letter size at a resolution of 240 dpi (dots per inch), the length-wise direction of which is put so as to orient the horizontal direction as is shown in FIG. 6(a) (hereinafter referred to "horizontally put paper"), there is used a memory having a memory area of 330 bytes (horizontal) * 2040 lines (vertical). Accordingly, as shown in FIG. 7(a), in order to access this memory, a horizontal counter 22 of 9 bits and a vertical counter of 11 bits are needed and, therefore, twenty address signal lines become necessary.
Similarly, in a case wherein print is made on the print paper laid normally in a vertical direction at a resolution of 240 dpi (hereinafter referred to "vertically put paper"), as is shown in FIG. 6(b), a memory having a memory area of 255 bytes (horizontal) * 2640 lines (vertical) is used. Accordingly, as shown in FIG. 7(b), a horizontal counter 22 of 8 bits and a vertical counter 23 of 12 bits are needed for accessing the memory, and therefore, twenty address signal lines become necessary.
If one wishes to provide a memory being available for both papers put horizontally and vertically, it should have a memory area of 330 bytes (horizontal) * 2640 lines (vertical) as shown in FIG. 6(c). Accordingly, as shown in FIG. 7(c), a horizontal counter 22 of 9 bits and a vertical counter 23 of 12 bits become necessary in order to access said memory, and therefore, twenty-one (21=9+12) address signal lines become necessary. In other words, the number of address signal lines in this case becomes more than that of either memories by one which are provided independently for respective papers put horizontally and vertically.
Roughly speaking, this difference by one address signal line means that the capacity of the latter case becomes almost twice that of the former case although, as shown in FIG. 6(c), areas a and c are not necessary in the case of the paper put vertically and areas b and c are not necessary in the case of the paper put horizontally.
One possible method to solve this problem is to provide one more counter of one bit as indicated by a reference numeral 24 in FIG. 8 which serves as a counter for the lower most bit of the horizontal counter in the case of the paper put horizontally and as a counter for the upper most bit of the vertical counter in the case of the paper put vertically. This counter 24 can be switched from the horizontal counter 22 to the vertical counter 23 or vice versa by a selector 25. This enables access to both memories with twenty address signal lines without increasing the capacities of memories.
This method is effective for handling both sizes of papers put vertically and horizontally.
However, when considering a system available to a variety of sizes of papers put horizontally and vertically and/or being able to switch the resolution from 240 dpi to 480 dpi, said method is not so effective because it is not flexible to an extention of the memory 21, complex structures of the selector 25 and horizontal and vertical counters 22 and 23 are required and, further, the memory 21, when extended, would contain a useless memory area.